Heating, cooling, and de-humidification systems within large buildings, such as grocery stores, are implemented to provide the multiple purposes of heating the building in winter, cooling the building in summer, cooling food products during both winter and summer and de-humidifying the building in the summer.
Normally, in the example of a grocery store, these systems are implemented independently of one another. For example, a primary food cooling system would be established to operate a grocery store's banks of freezers and coolers with its own system of refrigeration compressors, condensors and evaporators independently of a store's air conditioning system (having its own compressors, condensers and evaporators) which may also be independent of the store's heating system. In the summer, dehumidification systems may also be implemented to prevent the build-up of frost on food packages in open coolers or freezers.
With respect to a grocery store's cooling system for freezers and coolers, the evaporators or cooling coils of a food cooling system must be defrosted on a regular basis to ensure that the cooling system remains efficient. Specifically, refrigeration systems require frequent defrosting of the cooling coils of a freezer or cooler to remove frost which condenses on the cooling coils from the air passing over the cooling coils. In particular, open coolers or freezers are in contact with the air within a store and, accordingly, over time will circulate the humid air within the store through the cooler. On humid days, the condensation resulting from cooling can be substantial, resulting in significant frost build-up on both the cooling coils and the food products within the cooler/freezer. As frost builds up on the cooling coils, its effectiveness for cooling is reduced and, if left un-defrosted, will reduce the cooling efficiency of the cooler/freezer. Accordingly, regular defrosting of the coils is required to remove the frost from the coils. The defrosting cycle also contributes to the dehumidification of the store by the overall removal of water vapour from the atmosphere.
In a typical store, a defrost cycle is run every 6 hours wherein either the compressor is turned off and a defrost heater is activated to melt any condensed ice off the evaporator coils or the flow of refrigerant through the coils is reversed so that hot refrigerant is allowed to melt the frost build-up from the inside of the coil to the outside of the coil. In the case of an external heater, because heating is taking place externally and the heat transfer coefficient through air is low, the defrost cycle may take 30 minutes to complete such that the temperature within freezer or cooler may rise substantially thus increasing the risk of food spoilage as well as resulting in overall inefficient power consumption. During the defrost cycle, any melted water is allowed to drain away.
As indicated above, during this defrost process the temperature within the freezer/cooler may rise substantially to temperatures which affect the growth of micro-organisms on the food products resulting in an increased risk of food spoilage and the associated risk of food poisoning to the consumer. Furthermore, the repeated freeze--partial melt and re-freeze cycles in a freezer will have a significant impact on the shelf-life of the food products within the freezer often leading to a premature deterioration of the food and, hence, substantial wastage of the food. This leads to increased costs to both the store owner and consumer. In coolers, as opposed to freezers, this effect and the risk of food spoilage is more significant as the temperatures are higher.
In order to address the problems of inefficient defrost cycles, the use of water based cooling solutions have been proposed to provide a more efficient defrost cycle. In these systems, a gas-based refrigeration system is used to cool a water solution which is circulated through cooling cools in the freezer or cooler. The use of a water based solution for cooling has the effect of enabling rapid defrost cycles to be run, primarily as a result of the thermal mass of the water based solution. That is, in comparison with flowing a refrigerant gas through the cooling coils, the heat transfer coefficient for circulating a warm water-based liquid through the coiling coils is substantially greater than the heat transfer coefficient for circulating a warm refrigerant gas through the coiling coils.
Water based systems have permitted defrost cycles to be completed within a few minutes such that the temperature of the freezer or cooler does not rise to the same extent as with a refrigerant gas-based system. Furthermore, a water based cooling system allows a defrost cycle to be run every hour which minimizes the total amount of frost which may build up on a cooling coil over this time. This is compared to a gas based system which can only be defrosted every 4 hours or so due to the time required for a defrost cycle.
While a water based cooling system has advantages with respect to defrost cycles, the energy efficiency ratio (EER, measured in BTU(of cooling)/watts(energy utilized), and a measure of the cooling efficiency) remains similar to that of a conventional gas-based refrigeration system. In particular, refrigerant gas based cooling systems utilizing refrigerant gas to air heat transfer may have an EER in the order of 6 BTU/watt for a 0.degree. F. (cooler temperature) to 140.degree. F. (condenser temperature) thermal bridge while a water based cooling system utilizing water to air transfer under similar conditions would have a slightly lower EER.
As such, a number of problems exist with respect to prior art systems with respect to the ability of these systems to effectively provide efficient cooling of freezers and coolers, in combination with effective defrost systems, de-humidification systems and building heating and cooling systems.
For example, situations often exist where these independent systems work against one another or very inefficiently with respect to one another. This may involve, for example, air conditioners attempting to cool air including waste heat from a cooling system or defrosting system or waste heat from a cooling system not being utilized to heat the building in the winter.
Accordingly, there has been a need for a system which integrates all the heating and cooling systems of a building into an efficient system which effectively manages the transfer of heat between freezers, coolers, air conditioning, heating, dehumidification and defrost systems and in particular there has been a need for a system which does not allow the air temperature within a freezer/cooler to rise substantially during the defrost cycle and which allows for highly effective dehumidification of the building atmosphere. The development of such a system will also reduce the capital and maintenance costs associated with each of these systems.
Specifically, there has been a need for a geothermal based system integrated to the heating and cooling system of a building to provide improved overall system energy efficiency as well as a specific need for a dual flow path, water based cooling system which provides efficient defrosting cycles and which also provide effective dehumidification to a building atmosphere.
A review of the prior art has revealed that such a system has heretobefore not been realized. For example, U.S. Pat. No. 5,000,257 discloses a heat exchanger having a radiator and a condenser in proximal relationship with one another; U.S. Pat. 4,002,201 discloses a multiple fluid stacked heat exchanger; U.S. Pat. No. 4,176,525 discloses a combined environmental and refrigeration system for use in grocery stores and the like; U.S. Pat. No. 5,586,444 discloses a control system for multiple cooling case in a grocery store; U.S. Pat. No. 4,288,993 discloses a refrigeration system having primary and secondary refrigeration systems in heat exchanging contact with each other; U.S. Pat. No. 5,570,585 discloses a cooling system that operates to cool and store a product load having two compressor systems that are configured to operate independently or together as a single stage compressor; and, U.S. Pat. No. 4,191,024 discloses a defrosting method for use in a refrigeration system that alternately uses one of two coolers while the other is defrosting.